Conventionally, in a vehicle navigation apparatus, radio navigation and self-contained navigation are known as methods for measuring a vehicle current position. As represented by a global positioning system (GPS), the radio navigation is receiving information from a satellite or the like and calculating a vehicle current position (latitude and longitude) from the received information. The merit of the radio navigation is that the vehicle current position can be obtained as an absolute position while a radio wave is received. On the other hand, the demerit of the radio navigation is that a measurement position varies within a predetermined error range, and measurement of vehicle position cannot be performed in a tunnel or under an elevated road.
The self-contained navigation is calculating a vehicle current position by integrating a traveled distance calculated from a measurement signal from e.g. a vehicle speed sensor in accordance with a direction calculated from a direction sensor such as a gyro sensor or a geomagnetic sensor. The merit of the self-contained navigation is that the vehicle position can be always calculated without being influenced by environment. On the other hand, the demerit of the self-contained navigation is that the error of the sensor is accumulated and the error increases as the traveled distance increases. This is because the self position is obtained by integration of the traveled distance in accordance with direction.
Accordingly, a vehicle navigation apparatus to calculate a vehicle current position by hybrid navigation as a combination of the radio navigation and the self-contained navigation utilizing the merits of the both navigation systems is widely used. For example, as one example of the hybrid navigation, while a current position is calculated by the self-contained navigation, the current position is corrected based on latitude and longitude calculated by the radio navigation. This eliminates the influence of sensor error in the self-contained navigation.
Further, for more accurate current position calculation, map matching processing is widely adopted. The map matching processing is comparing latitude and longitude calculated by the hybrid navigation and a vehicle travel locus with road data stored in a map data base, thereby obtaining a more correct vehicle current position.
The principle of the map matching processing will be briefly described in accordance with FIGS. 7A, 7B and 7C. For example, all the roads connected to an intersection where a vehicle has arrived are selected as candidate roads with a possibility that the vehicle may pass through. In the example of FIG. 7A, roads a, b and c are selected as candidate roads. Note that a road existing outside a predetermined range with respect to latitude and longitude, as the reference, of output by the hybrid navigation is excluded from the candidate roads. The shape of each of the selected candidate roads is compared with the shape of the vehicle travel locus. A road with the highest correlativity is regarded as a road where the vehicle is traveling. The vehicle position is determined on the road. In the example of FIG. 7C, as the road b has the highest correlativity, it is considered that the vehicle is traveling on the road b, and the vehicle position is determined on the road b. This processing is performed by predetermined time or distance the vehicle traveled, and the vehicle position is always determined on a road.
As described above, the principle of the map matching processing is premised on vehicle's traveling a road. However, a vehicle does not always travel on a road. It may travel on an off-road area such as a dry riverbed or a mountainous area, a wide private property or a parking lot. In these cases, when map matching processing is performed, the vehicle position is erroneously determined on an adjacent road and an accurate vehicle position cannot be obtained. For this reason, a vehicle navigation apparatus described in Patent Document (JP-A-S58-162809), for example, is provided with a switch to select execution or stoppage of map matching processing. In a case where traveling on an off-road area, a parking lot or the like as described above is started, a vehicle driver can designate stoppage of map matching processing.
However, in the above-described conventional vehicle navigation apparatus, the selection is merely made between execution and stoppage of map matching processing. Accordingly, a switch operation must be performed every time a situation where the map matching processing should be executed is changed to a situation where the processing should be stopped, or vice versa. During vehicle traveling, the vehicle driver must perform the selection operation between the execution and stoppage of the map matching processing. Thus selection operation may become load on the driver.